1. Field of the Invention
The present invention generally relates to a continuously variable transmission with a V-belt for use in vehicles, etc., and more particularly to an improvement in shift control of the continuously variable transmission.
2. Description of the Prior Art
In recent years, there has been developed a so-called hybrid vehicle, which is a combination of an internal combustion engine (hereinafter referred to as an engine) and an electric motor, in order to protect the environment and improve the fuel economy. Accordingly, a combination of this hybrid vehicle and a V-belt type continuously variable transmission has been proposed.
In the V-belt type continuously variable transmission, a V-belt passes about a primary pulley and a secondary pulley, both of which are variable pulleys. The groove width of the primary pulley is variably controlled by the supply of hydraulic pressure.
More specifically, as shown in FIG. 5, a first cylinder chamber 20 and a second cylinder chamber 32 are provided to the primary pulley 16 and the secondary pulley 26, respectively. Line pressure is continuously supplied to the second cylinder chamber 32 of the secondary pulley 26. Hydraulic pressure, which is acquired by regulating the line pressure as original pressure with a shift control valve 63, is supplied to the first cylinder chamber 20 of the primary pulley 16. The hydraulic pressure supplied to the first cylinder chamber 20 changes the groove width of the primary pulley 16 to change the gear ratio. In the meantime, the line pressure is changed within a predetermined range to control a thrust (pushing pressure) against a V-belt 24.
To control the hydraulic pressure supplied to the first cylinder chamber 20, the shift control valve 63 driven by a step motor 64 regulates the line pressure as the original pressure.
More specifically, the shift control valve 63 has a primary port 63P connected with the first cylinder chamber 20, a line pressure port 63L supplied with the line pressure, and a drain port 63T. The shift control valve 63 also has a spool 63a, which slides according to the positions of a moving conical board 22 of the primary pulley 16 and the step motor 64. The displacement of the spool 63a causes the primary port 63P to selectively connect with the line pressure port 63L or the drain port 63T to thereby control the hydraulic pressure supplied to the first cylinder chamber 20.
Oil supplied to the primary pulley 16 is supplied as control hydraulic pressure to the first cylinder chamber 20, and is also supplied to a bearing 14 of the primary pulley 16 through an orifice in order to lubricate the bearing 14.
The continuously variable transmission of this kind is disclosed in, e.g., Japanese Patent Application Laid-Open Publication No. 11-82725.
The hybrid vehicle is equipped with a battery having a large capacity, and it is therefore easy to use the electric motor in various areas of a power system. For this reason, the electric motor preferably drives a hydraulic pump for use in lubricating each part of the engine and operating the continuously variable transmission because this achieves the stable rotation of the pump.
If the electric motor drives the hydraulic pump, however, the hydraulic pump stops functioning and supplying the line pressure when a failure occurs in a power supply system of the electric motor while the vehicle is running.
In this case, an alarm or the like is given to warn of the failure, and the vehicle is stopped to restore the system to a normal operating state. If the vehicle is driven again, however, the shift may not be performed normally.
According to a research, the above problem results from a slip between the variable pulleys and the V-belt.
It is therefore an object of the present invention to provide a continuously variable transmission, which prevents the slip between the variable pulleys and the V-belt even when the supply of the hydraulic pressure is temporarily stopped due to the failure in the power supply system of the electric motor that drives the hydraulic pump.
According to a further research about the slip, if the hydraulic pump stops to cease the supply of the line pressure, the step motor is controlled toward a Lo range (low range gear ratio) with the deceleration of the vehicle. Since the residual hydraulic pressure gradually gets out of a hydraulic circuit, the hydraulic pressure in the second cylinder chamber 32 of the secondary pulley is lowered. Consequently, the vehicle stops while the step motor cannot return to the position corresponding to the lowest gear ratio.
As time passes, the hydraulic pressure in the first cylinder chamber 20 of the primary pulley is further lowered. Moreover, if the oil is also supplied to the bearing 14, the hydraulic pressure leaks. Consequently, the oil is decreased in the first cylinder chamber 20.
Therefore, when the vehicle restarts running after the power supply system of the electric motor is restored to a normal operating state following the failure, the shift cannot be started from the lowest range ratio and there is hardly remained the pushing pressure of the pulleys against the V-belt. In addition, the shift is started with only a small amount of hydraulic pressure being supplied. This results in the slip between the pulleys and the V-belt.
To solve the above-mentioned problems, the present invention provides a control device of a continuously variable transmission which comprises: a transmission mechanism comprising a pair of variable pulleys with groove widths being changed by supply of hydraulic pressure, and a belt passing about the pair of variable pulleys; a hydraulic pump being driven by an electric motor to supply hydraulic pressure; line pressure control means for regulating hydraulic pressure from the hydraulic pump to predetermined line pressure; shift control means for outputting a shift command according to a driving state; and a shift control valve for supplying hydraulic pressure, whose original pressure is line pressure, to the pair of variable pulleys in the transmission mechanism according to the shift command; the control device of the continuously variable transmission further comprising: failure information holding means for holding failure information on a failure of the electric motor; and wherein if, at start of driving, the failure information holding means holds failure information indicating that the electric motor fails in previous driving, the shift control means outputs a predetermined shift command to thereby fill the variable pulleys with hydraulic pressure through the shift control valve.
If the electric motor fails in the previous driving of the vehicle, the variable pulleys are filled with the hydraulic pressure through the shift control valve. Accordingly, if no hydraulic pressure remains in the variable pulleys and it is therefore necessary to prevent the slip, the shift control valve is controlled to fill the variable pulleys with the hydraulic pressure to prevent the slip between the pulleys and the belt.
The present invention also provides a control device of a continuously variable transmission, which comprises: a transmission mechanism comprising a primary pulley and a secondary pulley provided with a first cylinder chamber and a second cylinder chamber, with groove widths being changed by supply of hydraulic pressure respectively, and a belt passing about the primary pulley and the secondary pulley; a hydraulic pump being driven by an electric motor to supply hydraulic pressure; line pressure control means for regulating hydraulic pressure from the hydraulic pump to predetermined line pressure and continuously supplying the line pressure to the second cylinder chamber; a shift control valve being driven by an actuator to supply hydraulic pressure, whose original pressure is line pressure, to the first cylinder chamber; and shift control means for outputting a shift command for controlling the actuator according to a driving state, the control device of the continuously variable transmission further comprising: failure information holding means for holding failure information on the failure of the electric motor; and wherein if, at start of driving, the failure information holding means holds failure information indicating that the electric motor fails in previous driving, the shift control means outputs a shift command targeting a high range ratio to thereby fill the first cylinder chamber of the primary pulley with hydraulic pressure.
The shift control valve is controlled to fill the first cylinder chamber with the hydraulic pressure according to the shift command targeting the high range ratio. This reduces the groove width of the primary pulley, and eliminates a clearance between the primary and secondary pulleys and the belt, thus preventing the slip.
In one preferred form of the present invention, the first cylinder chamber is filled with hydraulic pressure by holding a shift command targeting a high range ratio for a predetermined period of time.
The predetermined period of time is found in advance by conducting an experiment, and the shift command is held for the predetermined period of time. Therefore, the first cylinder chamber can be filled with the hydraulic pressure without fail.
The present invention also provides a control device of a continuously variable transmission in a vehicle, which control device comprises: a transmission mechanism comprising a primary pulley and a secondary pulley provided with a first cylinder chamber and a second cylinder chamber, respectively, and a belt passing about the primary pulley and the secondary pulley with groove widths being changed by supply of hydraulic pressure; a hydraulic pump being driven by an electric motor to supply hydraulic pressure; line pressure control means for regulating hydraulic pressure from the hydraulic pump to predetermined line pressure and continuously supplying the line pressure to the second cylinder chamber; a shift control valve being driven by an actuator to supply hydraulic pressure, whose original pressure is line pressure, to the first cylinder chamber; and shift control means for outputting a shift command for controlling the actuator according to a driving state, the control device of the continuously variable transmission comprising: failure information holding means for holding failure information concerning a failure of the electric motor; and wherein if, at start of driving, the failure information holding means holds failure information indicating that the electric motor fails in previous driving, the shift control means outputs a shift command targeting a high range ratio for a predetermined period of time before the start of driving to thereby fill the first cylinder chamber of the primary pulley with hydraulic pressure, and start outputting a shift command targeting a normal gear ratio according to the driving state after a predetermined vehicle speed is reached after the start of driving.
As mentioned above, the control for preventing the slip transits to the normal shift control after the predetermined vehicle speed, which enables the stable detection of the input/output revolutions, etc., is reached. This eliminates the possibility of instability during the transition from the control for preventing the slip to the normal shift control.
In another preferred form of the present invention, a motor control unit controls the electric motor; the failure information holding means is an internal memory of the shift control means, which retains a heavy-current system fail flag according to the failure information received from the motor control unit; and the heavy-current system fail flag is reset after the predetermined vehicle speed is reached.
As mentioned above, the shift control means holds the failure information concerning the failure in the previous driving of the vehicle, and it is therefore possible to quickly execute the control for preventing the slip without waiting for a command or the like from other control unit. It is also possible to prevent the unnecessary repetition of the control for preventing the slip when the vehicle is driven next time, because the heavy-current system fail flag representing the failure information is reset after the execution of the control for preventing the slip.